Optical biosensors are a class of instruments that can detect intramolecular interactions in real-time, without labels, and with high sensitivity. Their use has grown at a 25-40 percent annual rate since the early 1990's, and biosensors have been integrated into both drug development and diagnostics. However, optical biosensors have yet to be used with membrane proteins, a family of biological molecules that composes nearly half of current drug targets. The nature of biosensor detection restricts nearly all such devices to soluble molecules, and removal of membrane proteins from their native lipid environment destroys their structure. Ligand interactions with membrane proteins are responsible for a multitude of cell adhesion, signaling, and regulatory events. This diversity of function makes membrane proteins, such as G-protein coupled receptors (GPCRs), important drug targets. Integral Molecular has developed a technology, the lipoparticle, based on retroviral structure that enables membrane proteins to be purified away from the surface of a cell while maintaining their structural integrity. In preliminary research, we demonstrated that lipoparticles can be produced with a diverse range of membrane proteins, retain the structure of those proteins, and can be used with biosensors for measuring binding interactions with GPCRs. The experimental objectives of our Phase I SBIR to integrate lipoparticles and biosensors have recently been successfully completed. Major sources of variability were optimized, including immobilization, regeneration conditions, and buffer conditions. Performance was evaluated for potential commercial applications, including specificity, sensitivity, and reproducibility. The product that results from these studies is expected to be used for research, diagnostics, and the development of therapeutic proteins and antibodies. In the current proposal, our Specific Aims are to: I) Improve Lipoparticie-Biosensor Integration, II) Visualize Lipoparticles on the Biosensor Surface, and III) Conduct Proof-of-Concept Applications.